1. Field of the Invention
The present invention relates to display apparatuses sealed with an organic protective film and an inorganic protective film.
2. Description of the Related Art
Recently, display apparatuses using self-emitting organic light-emitting elements have attracted attention as thin, lightweight display apparatuses. One of the major problems with display apparatuses using organic light-emitting elements is their resistance to moisture and oxygen. If moisture and oxygen intrude into a display apparatus, they degrade the organic compound layer material constituting the organic light-emitting elements and form dead regions, called dark spots, in the display apparatus, thus decreasing the display performance thereof.
As a solution for improving the resistance of a display apparatus to moisture and oxygen, there is a known seal structure formed by stacking an organic protective film and an inorganic protective film. In this seal structure, the inorganic protective film blocks moisture, and the organic protective film is provided to smooth irregularities in the surface of the display apparatus so that no defect occurs in the inorganic protective film. Accordingly, the organic protective film is formed so as to cover at least a region where organic light-emitting elements are provided, whereas the inorganic protective film is formed in a larger area than the organic protective film so as to cover the organic protective film and so as to contact a member formed of an inorganic material and disposed below the organic light-emitting elements in a region surrounding the organic protective film. This prevents intrusion of moisture from the surface of the organic protective film, from the region surrounding the organic protective film, and from the bottoms of the organic light-emitting elements.
Japanese Patent Laid-Open No. 2005-251721 (Patent Document 1), relating to a technique for forming an organic protective film (buffer layer) by a wet process (coating process), discloses a display apparatus having a frame portion for stopping an organic protective film material from flowing out of a predetermined region. This allows the organic protective film to be formed only in the necessary region, thus ensuring a sufficient region surrounding the organic protective film where the inorganic protective film contacts a member formed of an inorganic material and disposed below the organic light-emitting elements.
A film formation technique based on a wet process such as dispensing or printing is advantageous in terms of cost over a film formation technique based on a dry process using a vacuum device, although it has the problem described below.
FIG. 8 is a schematic sectional view of an end of a display apparatus sealed by stacking an organic protective film 10 and an inorganic protective film 11. The organic protective film 10 is formed so as to cover a display region A. The inorganic protective film 11 is formed in a region larger than the organic protective film 10 so as to cover the organic protective film 10 and so as to contact a support substrate 1 in a region surrounding the organic protective film 10. In this case, the support substrate 1 is formed of an inorganic material.
If the organic protective film 10 is formed by a wet process, a sloped portion B is formed at the end thereof, depending on the viscosity of the organic protective film material and its wettability to the support substrate 1. For example, if the position where the end of the organic protective film 10 is formed is set to a position E shifted outward from the display region A by the width b of the sloped portion B, the end of the organic protective film 10 is formed at an uncertain position between a position F shifted from the position E to the display region side by a distance of m and a position G shifted to the opposite side by a distance of m because the positional accuracy of film formation by a wet process involves an error of ±m. If the end of the organic protective film 10 is formed at the position F, the sloped portion B of the organic protective film 10 overlaps the display region A. This results in image degradation at the sloped portion B because it locally distorts a reflection of external light. Therefore, the organic protective film 10 must be formed so that the sloped portion B does not overlap the display region A.
Accordingly, one possible approach is to set the position where the end of the organic protective film material is formed to a position G separated from the position E to the side away from the display region A by a distance of m so that the end of the organic protective film 10 is not located inside the position E even if the position thereof deviates most to the display region side due to a process error. In this case, the width d required for the region outside the display region A (frame region) is represented by the following inequality:d≧b+2m+c  (1)where c is the width required for a region surrounding the organic protective film 10 where the inorganic protective film 11 contacts a member formed of an inorganic material and disposed below the organic light-emitting elements. Inequality (1) suggests that, taking into account an error due to a wet process, namely, ±m, an extra width of 2 m is required in addition to the minimum width required for the frame region, namely, b+c.
According to Patent Document 1, by providing a frame portion and applying an organic protective film material with high liquidity, the end of the organic protective film can be reliably formed in a predetermined region while preventing the organic protective film material from flowing out of the predetermined region. This eliminates the need for taking the error m into account in the application of the organic protective film material. However, to form an organic protective film having a thickness sufficient to smooth irregularities in the surface of the display apparatus with a material with high liquidity, it is necessary to form a frame portion having a height equivalent to the thickness of the organic protective film. According to Patent Document 1, the frame portion is provided at a predetermined position by dispensing or screen printing using a highly viscous material. This requires an extra width taking into account an error due to a wet process, namely, 2 m, for the frame region in the step of providing the frame portion, thus resulting in the same problem as before. In addition, this technique has a problem in that the materials applicable to the organic protective film are limited because the material used requires a viscosity of about 1 to 30 cp so that it can be spread to the frame portion.
Display apparatuses using organic light-emitting elements are often used for displays of mobile devices because a reduction in thickness and weight is possible. In addition to a reduction in thickness and weight, forming a narrow frame region, that is, a reduction in frame width, and a reduction in cost are major challenges for displays of mobile devices; the technique disclosed in Patent Document 1 does not achieve a sufficient reduction in frame width.